In the fabrication of printed wiring boards and/or printed circuit boards, soldering is the preferred technique for electrically connecting components. Soldering fluxes are first applied to the substrate board material to insure firm, uniform bonding of the solder. While both rosin and non-rosin soldering fluxes are available, rosin fluxes are preferred because they are less corrosive, and have a much longer history of use. Non-rosin, water-soluble fluxes are a more recent development. However, these non-rosin fluxes contain strong acids and/or amine hydrohalides and are thus corrosive, and can cause circuit failure if residual traces are not carefully removed.
Batch-type or underbrush cleaners were initially employed to remove rosin and non-rosin fluxes from printed wiring boards and/or printed circuit boards after soldering. Later, in-line solvent cleaners were adopted to meet demands of increased throughput.
The removal of rosin fluxes from printed circuit boards or printed wiring boards has traditionally been accomplished using chlorinated hydrocarbon and chlorofluorinated solvents, such as 1,1,1,-trichlorethane, trichloromonofluoromethane, methylene chloride, trichlorotrifluoroethane, methyl chloroform, and CFC 113. By the early 1970s, aqueous cleaners using alkaline cleaning compounds, such as the alkanol amines, usually in the form of monoethanolamine, were adopted for rosin flux removal as an alternative to the toxic chlorinated hydrocarbon and chlorofluorinated solvents. These aqueous cleaners chemically react with the rosin flux to form a rosin soap through the process of saponification. Other organic substances, such as surfactants or alcohol derivatives, may be added to these alkaline cleaning compounds to facilitate the removal of such rosin soap. During the past few years, in response to environmental concerns, alternatives have emerged, such as terpene compounds, which are readily biodegradable. An example of such a compound is described in U.S. Pat. No. 4,640,719.
Regardless of which solvent is used, typically the solvent is sprayed onto the printer circuit boards and/or printed wiring boards through some type of a sprayer or nozzle assembly, preferably with sufficient force to dislodge rosin fluxes and to penetrate small spaces between the board and devices mounted thereto. Moreover, especially when terpene compounds are used, after being washed with solvents, the boards must be rinsed, typically with water, to remove the solvents. Water is sprayed onto the boards through some type of sprayer or nozzle assembly, preferably with sufficient force to remove all of the solvents from the board. In both instances, the nozzles or sprayers must cover the entire board with water or solvent. It is also desirable that some of this spray strike the board at an angle with respect to the vertical and with sufficient force, so that water or solvents can penetrate into spaces between the board and devices, and so that fluxes are more readily dislodged.
Existing nozzle or sprayer assemblies typically spray the solvent or water from a nozzle head by passing it through a plurality of holes. These holes distribute the liquid or solvent to provide the desired horizontal coverage, as well as the desired angle of attack of the spray. However, because the nozzle head forces the liquid stream against the perforated barrier which divides the stream into a plurality of smaller streams, the force of the stream is considerably lost, and the velocity of the individual streams striking the board or other device is not optimized.
Typically, apparatus used to wash the boards with a solvent is mounted in an in-line relationship with the soldering apparatus, and a continuously moving conveyor transports the boards from the soldering apparatus and through the washing apparatus from one end to the other. If a rinsing apparatus is also provided it is disposed in an in-line relationship with the washing apparatus. A conveyor transports the hoards from the washing apparatus and through the rinsing apparatus from one end to the other. The same conveyor is sometimes used to convey the boards through both the washing and rinsing apparatus.
It is therefore an object of the present invention to provide apparatus for spraying printed circuit boards, printed wiring boards or other like product loads with an optimal, high-velocity stream of liquid.
It is another object of the present invention to provide apparatus for spraying product loads with a liquid spray which forms an angle with respect to the vertical.
It is a further object of the present invention to provide liquid sprayer heads with sufficient horizontal breadth that the entire surface of a product load passing therebeneath is covered with liquid.
It is yet another further object of the present invention to provide such a liquid sprayer configured to be used in apparatus for washing or rinsing printed circuit boards after completion of a soldering operation.